Assuming he means the half life in terms of radioactive isotope decay that would mean the power source is Curium-246.
Curium sits right between holmium and carbon-14 in terms of half life, at 4730 years. There are no other isotopes around the 5000 year half life mark, apart from these three.
Interestingly, where holmium and carbon-14 isotope decay yields almost no energy, curium decay yields very high energies.
Infact curium is used as fuel in radioisotope thermoelectric generators on board spacecraft:
https://en.wikipedia.org/wiki/Radioisot ... _generator
Also curium decays with α-particle radiation which is a lot safer to humans than isotopes that decay using much more dangerous beta radiation (gamma/X-rays). That is another reason why curium has practical application uses in spacecraft as opposed to isotopes of e.g. radium, or uranium.
It's crazy how specific Aykroyd's science is when you look for it.
PS: You'll note the pressure venting device in the illustration above.